void main(List<String> args) {
  List goodsList = [
    {"id": 1, "price": 22.68, "count": 3, "goods_name": "西瓜", "selectd": true},
    {"id": 2, "price": 11.99, "count": 3, "goods_name": "草莓", "selectd": true},
    {
      "id": 3,
      "price": 60.99,
      "count": 1,
      "goods_name": "车厘子",
      "selectd": false
    },
    {
      "id": 4,
      "price": 11.68,
      "count": 3,
      "goods_name": "平谷大桃",
      "selectd": false
    }
  ];

  double allValue = goodsList.where((element) => element['selectd']).fold(0,
      (previousValue, item) => previousValue + item['price'] * item['count']);
  print(allValue);
}
